The present disclosure relates to a communication state display method and a communication state display device that allow the communication state in general-purpose serial communication to be checked by lighting of an indicator such as an LED.
In the past, general-purpose serial communication (RS232, RS485, and the like) has generally been used for communication between, for example, industrial apparatuses. Features of each type of serial communication are shown in Table 1 (see “Feature comparison between RS232/RS422/RS485,” NIHON ELECTRIC WIRE & CABLE CO., LTD.,
<http://www.nihondensen.co.jp/?p=376>).
TABLE 1RS232RS422RS485Transmission pathUnbalancedBalancedBalancedTransmissionMinimumSpeed—Not more than 90 kbpsNot more than 90 kbpsspeedDistance—1200 m1200 mMaximumSpeed19.2 kbps10 Mbps10 MbpsDistance—15.2 m15.2 mConnectorD-sub25 pinNot specifiedNot specifiedD-sub9 pinTermination resistor—One terminal (input side)Both terminalsConnectable numberPoint-to-pointMultidropMultidrop(1 to 1)(1 to 10)(Multi-to-multi: 32 at most)Communication systemFull duplexFull duplexHalf duplex
An industrial apparatus having a serial communication function may use an indicator such as a light emitting diode (LED) to display the physical transmission state and reception state in order to check the serial communication wiring, for example. Examples of a method of displaying communication state include (1) a method of driving an indicator such as an LED with a transmission signal or reception signal for serial communication and (2) a method of driving an indicator such as an LED by a controller such as a central processing unit (CPU) incorporated in an industrial apparatus to display the communication state of the controller.
As the method (2), a serial communication system in which the wiring can be checked by outputting, by the CPU of a control unit, a checking signal to a plurality of terminal units connected to a serial signal line, returning, by each terminal unit, the number of channels of their own in response to the checking signal, and listing, by a host controller connected to the control unit, the received number of channels is proposed (see Japanese Patent Application Laid-open No. 2002-369272). It should be noted that the method (2) needs a CPU and the like, resulting in complicated structure. On the other hand, the method (1) is superior in that it does not use resources such as capabilities of the CPU and programs to display the communication state.